import java.util.*;

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 *   public TreeNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution7 {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param root TreeNode类 
     * @param o1 int整型 
     * @param o2 int整型 
     * @return int整型
     */
    public int lowestCommonAncestor (TreeNode root, int o1, int o2) {
        // write code here
        return fun(root,o1,o2);
    }
    public int fun(TreeNode root, int o1, int o2){
        if(root == null){
            return -2;
        }
        int left = fun(root.left,o1,o2);
        int right = fun(root.right,o1,o2);
        if(left >= 0){
            return left;
        } else if(right >= 0){
            return right;
        } else if(left == -1 && right == -1){
            return root.val;
        } else if(left == -1 || right == -1){
            if(root.val == o1 || root.val == o2){
                return root.val;
            } else {
                return -1;
            }
        } else {
            if(root.val == o1 || root.val == o2){
                return -1;
            }
            return -2;
        }
    }
}